Various types of polyurethane foams require blowing (expansion) agents for their manufacture. Historically, polyurethane foams used CFCs (chlorofluorocarbons) and HCFCs (hydrochlorofluorocarbons) as the primary blowing agents. CFCs have fallen into disfavor due to the implication of chlorine-containing molecules in the destruction of stratospheric ozone. Further, the production and use of CFCs has been restricted by the Montreal Protocol. HCFCs have been proposed as CFC substitutes, and are currently employed as foam blowing agents. However, HCFCs have also been shown to contribute to the depletion of stratospheric ozone, and as a result their use has come under scrutiny. The widespread use of HCFCs is scheduled for eventual phase out under the Montreal Protocol.
Hydrofluoroolefins (HFOs) represent a class of compounds being used as blowing agents in polyurethane and related foams that have a low global warming potential. Processes for the manufacture of HFOs have been previously described (e.g., U.S. Pat. Publ. No. 2007/152200 describes fire extinguishing and fire suppression compositions comprising unsaturated fluorocarbons and methods of preparing the HFOs). U.S. Pat. No. 8,461,401 describes a method for making haxafluoro-2-butene (HFO-1336). However, this method suffers from yield loss when performed in the liquid phase. To minimize yield loss in the first step of the process, a vapor phase process is employed. The overall process involves one liquid phase step and two gas phase steps. The cost for employing gas phase reactors can be high.
Thus, there is a need for a process for preparing HFOs, particularly HFO-1336, that reduces costs yet results in improved yields. There is also a need for a process for preparing HFOs that can be done in one phase, for example, the liquid phase.